The 3GPP (English full name: 3rd generation partnership project), a mobile communications standardization organization, proposes an enhanced NB-IoT (English full name: narrowband internet of things) subject. Positioning is one of main research content of the subject.
Currently, there are diverse positioning technologies. An OTDOA (English full name: observed time difference of arrival) positioning technology is one of technologies on which the enhanced NB-IoT subject focuses. FIG. 1 is a schematic diagram of an OTDOA positioning technology. In the OTDOA positioning technology, a plurality of base stations 01 send synchronization signals to a terminal device 02, and the terminal device 02 obtains arrival time information by measuring the synchronization signals sent by the plurality of base stations 01. Then, a geographical location of the terminal device 02 is obtained through calculation with reference to geographical locations of the plurality of base stations 01.
Specifically, an NSSS (narrowband secondary synchronization signal) is sent in NB-IoT in downlink, and the terminal device obtains arrival time information of downlink signals of a plurality of cells by measuring NSSSs of these cells, so as to support OTDOA positioning. Further, the terminal device determines the NSSS by detecting an NSSS sequence, and an expression manner of the NSSS sequence is
            d      ⁡              (        n        )              =                            b          q                ⁡                  (          m          )                    ⁢              e                              -            j                    ⁢                                          ⁢          2          ⁢                      πθ            f                    ⁢          n                    ⁢              e                              -            j                    ⁢                                    π              ⁢                                                          ⁢                                                un                  ′                                ⁡                                  (                                                            n                      ′                                        +                    1                                    )                                                      131                                ,where
n=0, 1, . . . , 131;
n′=n mod 131;
m=n mod 128;
u=NIDNcell mod 126+3;
      q    =          ⌊                        N          ID          Ncell                126            ⌋        ;and
bq(m) is a binary sequence, e−j2πθfn is a phase rotation sequence, a phase rotation parameter is θf=33/132(nf/2)mod 4, and nf is a radio frame number of a radio frame in which the NSSS is located.
When detecting the NSSS sequence, the terminal device needs to separately detect the binary sequence bq(m) and the phase rotation sequence e−j2πθfn. For the phase rotation sequence e−j2πθfn in frequency domain, a cyclic value of the phase rotation parameter θf is represented as a cyclic shift when the cyclic value is reflected in time domain. Therefore, when detecting the phase rotation sequence e−j2πθfn, the terminal device cannot distinguish phase rotation. Consequently, a relatively large error occurs in a timing measurement result, thereby further decreasing positioning precision. In addition, computational complexity is relatively high because phase rotation sequences need to be compared one by one.